OUACHITA, MARATHON, AND COAHUILA SYSTEMS 



225 



-^r 



PRE-MISSISSIPPIAN 

 FORMATIONS 



r^L. 



Fig. 14.2. Generalized structure map of the Ouachita and Arbuckle Mountains. MC, Magnet Cove. 



the Arbuckle Mountains. The Ouachita facies is characterized by an 

 abundance of silica in the pre-Mississippian formations and by the very 

 thick Carboniferous clastic sequences. Also it appears that incipient 

 metamorphism is included by some as a mark of the facies. This is all 

 a misuse of the term facies as defined, but for local paleogeologic studies 

 it is convenient, if properly understood. 



Structure 



The Ouachita Mountains may be divided into a western division, re- 

 plete with thrust faults, and an eastern division, intensely folded but 

 not appreciably faulted. 



According to Miser (1929) there are five thrust sheets in the Okla- 

 homa Ouachitas (see cross section D-D', Figs. 14.1 and 14.4), but in 

 light of Hendricks' additional work there are four "independent" 



thrusts. They are, from northwest to southeast: (1) the Choctaw fault, 

 (2) the Pine Mountain fault, (3) the Ti Valley fault, and (4) the Wind- 

 ingstair fault. See Fig. 14.5. Each sheet has been thrust from south to 

 north and has been broken by numerous smaller, high-angle reverse 

 faults that presumably join the main thrusts at depth. Minor cross faults 

 are numerous, and larger cross faults are present in several settings. The 

 stratigraphy of each thrust sheet is somewhat different and is sum- 

 marized in Fig. 14.3. 



In front of the thrust sheets is the Arkansas Valley basin whose beds 

 have been cast into open folds which gradually decrease in intensity 

 toward the north. These folds partake of some of the characteristics (4 

 both its bounding provinces, the beds on the south being rather close!) 

 folded near the Ouachitas but progressively more open farther north 

 toward the Ozark dome. Normal faults on the north side of the valley 



